1. Field of the Invention
The present invention relates to an internal combustion engine with novel cooling passages located within the cylinder head.
2. Disclosure Information
Liquid-cooled internal combustion engines have been in continuous use for more than a century. In the beginning, cooling systems for single cylinder engines relied upon a reservoir incorporated in the cylinder of the engine to flood an external portion of the cylinder with water, which was allowed to boil off. Later cooling system designs, although using radiators, employed steam generated within the engine to force the coolant through various passages. Finally, pumped cooling came to the fore.
The demands placed on engine cooling systems, defined to include the various cooling passages within the cylinder block and cylinder head of an engine, are not too great in the case of engines which are operated at low specific output. However, engines which are operated at high levels of specific output require large amounts of fuel, and therefore place heavy demands on their cooling systems. Moreover, cooling system design is critical with respect to particular areas of an engine's cylinder head, such as the bridge area extending between adjacent valves. This bridge area is particularly prone to thermal stress and cylinder head fire deck cracking, in the case of either two-valve engines with a single intake and exhaust in each cylinder head unit, or with multiple valve engines having, for example, two intake valves and a single exhaust valve, or even engines with two or more intake valves and two or more exhaust valves.
As used herein, the term “cylinder head unit” means a specific portion of a cylinder head having a single combustion chamber dedicated to a single engine cylinder. Thus, a cylinder head for a four-cylinder inline engine would have four cylinder head units. Following this convention, a cylinder head for a V-6 engine would have three cylinder head units.
A cylinder head having directed cooling according to the present invention permits operation at high specific output by applying the circulating coolant to the areas of the cylinder head which are either subject to the greatest heat flux, measured in terms of units of heat energy per unit of surface area, or which are prone to damage, such as the previously mentioned bridge area extending between adjacent valves in a given cylinder head unit. As a result, the present cylinder head is said to have “directed” cooling.